21078138 has 8 divisors (see below), whose sum is σ = 42156288. Its totient is φ = 7026044.

The previous prime is 21078131. The next prime is 21078149. The reversal of 21078138 is 83187012.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

21078138 is an admirable number.

It is not an unprimeable number, because it can be changed into a prime (21078131) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1756506 + ... + 1756517.

It is an arithmetic number, because the mean of its divisors is an integer number (5269536).

Almost surely, 2^21078138 is an apocalyptic number.

21078138 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21078138 is a wasteful number, since it uses less digits than its factorization.

21078138 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3513028.

The product of its (nonzero) digits is 2688, while the sum is 30.

The square root of 21078138 is about 4591.0933338367. The cubic root of 21078138 is about 276.2341795298.

The spelling of 21078138 in words is "twenty-one million, seventy-eight thousand, one hundred thirty-eight".